The present invention relates generally to medical devices and methods, and more particularly to transluminally implantable vascular blocking devices and methods for causing retrograde flow of arterial blood through veins to treat ischemia caused by insufficient arterial blood flow.
Atherosclerotic cardiovascular disease remains a major cause of premature death and morbidity, in most regions of the world. In addition to drug therapy, there currently exist a number of surgical and interventional techniques for treating atherosclerotic cardiovascular disease. Among these are a number of revascularization procedures wherein arterial or oxygenated blood (i.e., blood that generally has a pO2 of at least 50 and typically 75-100 while the patient is breathing room air) is rerouted or caused to flow in a manner that provides improved perfusion of ischemic tissues.
1. Surgical Bypass of Diseased Coronary or Peripheral Arteries
An arterial bypass graft operation is a type of surgery that is done to reroute or xe2x80x9cbypassxe2x80x9d blood around clogged arteries, thereby improving the supply of blood and oxygen to tissues that have become ischemic due to blockage(s) in the affected artery. During bypass surgery, surgeons take a blood vessel from another part of the body, or a synthetic or natural vascular graft, and construct a detour around the blocked part of a coronary or peripheral artery. In coronary artery bypass graft surgery (CABG) procedures performed to remedy an obstructed coronary artery, an artery (e.g., the right internal mammary artery or left internal mammary artery) may be detached from the chest wall and the open end of that detached artery is then attached to the coronary artery below the blocked area. Alternatively, a segment of a long vein may be harvested from the patient""s leg (e.g, Saphenous Vein) or other area of the body and one end of that vein segment connected to the aorta and its other end is attached or xe2x80x9cgraftedxe2x80x9d to the coronary artery below the blocked area.
Occasionally, because many coronary or cardiac veins are substantially parallel to coronary arteries, it happens that arterial bypass grafts are accidentally attached to a coronary or cardiac vein instead of the desired coronary artery. This results in the formation of inadvertent arterio-venous fistulas and resultant steal of arterial blood from the affected coronary vein due to shunt effect (i.e., oxygenated blood that has entered the vein flowing in the direction of normal venous bloodflow back to the right atrium instead of flowing in a direction opposite normal venous blood flow and perfusing the ischemic myocardium). These inadvertent arterio-venous fistulas have required corrective surgery to ligate the erroneously placed graft (thereby eliminating the shunt) and to create a new bypass graft that is connected to the intended coronary artery. see, Lawrie, G. M. et al., Aortocoronary Saphenous Vein Autograft Accidentally Attached to a Coronary Vein: Follow-up Angiography and Surgical Correction of the Resultant Arteriovenous Fistula, Ann. Thorac. Surg. 22:1 87-90 (1976).
Cardiovascular surgeons have also experimented with the purposeful use of cardiac veins for coronary revascularization. These coronary vein bypass graft (CVBG) procedures were typically performed on patients who had severely diffuse stenotic coronary artery disease that rendered them not to be candidates for mainstream CABG surgery. This CVBG technique involved using an intervening graft from the internal mammary artery or an aortic attachment to a saphenous vein graft. Instead of anastomosing the grafts to the distal coronary artery, the grafts were attached to coronary or cardiac veins that are generally parallel to the obstructed arteries. The coronary vein to which the graft is attached is then ligated proximal to the graft attachment to prevent a shunt. Thus, the veins were xe2x80x98arterializedxe2x80x99, allowing arterial blood to flow through the vein in a retrograde fashion in a effort to bring oxygenated blood to the venules and capillaries of the heart. However, the ligating of the vein proximal to the graft attachment (i.e., between the location at which the graft is anastomosed to the vein and the coronary venous sinus) often required dissection of the vein or tunneling under the vein to free the region of vein that is to be ligated from the myocardium. Such dissection and freeing of the vein can cause undesirable trauma to the myocardium. see, Hochberg, M. S., et al., Selective Arterialization of Coronary Veins: Clinical Experience of 55 American Heart Surgeons; Clinics of CSI; 1986, 1:195-201 (1986).
Furthermore, accomplishing a specific degree of partial or total closure of the vein can be difficult to accomplish by merely tying a ligature or suture around the vein. Indeed, if the ligature is drawn and tied too tightly the vein may be severed or perforated causing hemorrhage. On the other hand, if the ligature is drawn and tied too loosely the vein lumen may not become or remain permanently closed and the ligature may fail to stop the undesirable steal of arterial blood from the vein.
2. Catheter-Based Transluminal Procedures for Bypass of Diseased Coronary or Peripheral Arteries:
Included among the newer interventional techniques are certain percutaneous, transluminal techniques for bypassing obstructions in coronary or peripheral arteries through the use of the adjacent vein(s) as in situ bypass conduit(s); (e.g. using catheters to perform extraluminal procedures outside the diseased vessel lumen). These are proprietary procedures being developed by Transvascular, Inc. of Menlo Park, Calif. and are described in various publications including U.S. Pat. No. 5,830,222 (Makower) and U.S. Pat. No. 6,068,638 (Makower), as well as in published PCT Applications WO 98/16161 and WO 98/46119.
In one such procedure known as a Percutaneous In Situ Coronary Venous Arterialization (PICVA(trademark)), catheters are used to form an interstitial channel between a coronary artery or chamber of the heart and a coronary vein such that arterial or oxygenated blood (i.e., blood that generally has a pO2 of at least 50 and typically 75-100 while the patient is breathing room air) will flow from the artery or chamber of the heart and into the vein. A blocker delivery catheter is advanced into the vein, proximal to the location at which the channel is formed (i.e., between the location at which the channel is formed and the coronary venous sinus), and a radially expandable vessel blocking device is deployed from the catheter such that it becomes implanted in the lumen of the vein. This vessel blocking device serves to substantially block the flow of blood through the vein in the proximal direction (i.e., the direction in which venous blood normally flows through the vein, thereby eliminating the shunt effect and causing the arterial blood to flow through the vein in the distal direction (i.e., the direction opposite normal venous blood flow).
In another procedure known as Percutaneous In Situ Coronary Artery Bypass (PICAB(trademark)), catheters are used to form a first interstitial channel between a coronary artery or chamber of the heart and a coronary vein such that arterial or oxygenated blood (i.e., blood that generally has a pO2 of at least 50 and typically 75-100 while the patient is breathing room air) will flow from the artery or chamber of the heart and into the vein and a second interstitial channel between the vein into which the oxygenated blood is flowing and a distal segment of the obstructed coronary artery, downstream of the obstruction. A blocker delivery catheter is advanced into the vein and used to implant two (2) radially expandable vessel blockers, one proximal to the first interstitial channel (i.e., between the first channel and the coronary venous sinus) and another distal to the second interstitial channel (i.e., between the second channel and the capillary bed that is drained by the vein). The first vessel blocking device serves to substantially block the flow of blood through the vein in the proximal direction (the direction of normal venous blood flow), thereby eliminating the shunt effect and causing the arterial blood to flow through the vein in the distal direction (i.e., the direction opposite normal venous blood flow). The second vessel blocking device serves to cause the oxygenated blood that has been rerouted into the segment of vein between the first and second channels to flow through the second channel and into the obstructed artery, downstream of the obstruction. In this manner, oxygenated blood is caused to flow through the distal segment of the obstructed artery, thereby perfusing the previously ischemic tissue.
Although the prior art had included a number of embolic coils and other embolic devices for occluding blood vessels, those prior art embolic devices were not designed for use in arterialized veins and were found to be less than optimal for use in blocking arterialized veins in the PICVA and PICAB procedures. Accordingly, a number of specialized, transluminally insertable apparatus for closing the lumen of a blood vessel have been invented for use in the PICVA and PICAB procedures and are described in U.S. Pat. No. 6,071,292 (Makower et al.) entitled Transluminal Methods and Devices for Closing, Forming Attachments to, and/or Forming Anastomotic Junctions in Luminal Anatomical Structures and PCT International Publication Nos. WO97/27893 (Evard, et al.) entitled Methods and Apparatus for Blocking Flow Through Blood Vessels and WO99/49793 (Flaherty et al.) entitled Catheters, Systems and Methods for Percutaneous In Situ Arterio-Venous Bypass, the entire disclosures of which are expressly incorporated herein by reference. Given the potential usefulness of surgical CVBG procedures and the incidence of inadvertent arterio-venous fistula creation during CABG procedures, there exists a need in the art for the adaptation and use of the transluminally insertable lumen blocking apparatus such as those described in the aforementioned U.S. Pat. No. 6,071,292 (Makower et al.) and PCT International Publication Nos. WO97/27893 (Evard, et al.) and WO99/49793 (Flaherty et al.) in conjunction with surgical CVBG procedures and as a non-surgical means for eliminating xe2x80x9cstealxe2x80x9d of arterial blood from the vein and improving myocardial perfusion in patients who have experienced inadvertent arterio-venous fistula creation during CABG procedures.
The present invention provides percutaneous, transluminal (e.g., catheter-based) methods and devices for blocking the lumen of a vein into which oxygenated blood having a pO2 of at least 50 has been or will be caused to flow, as a result of the inadvertent or purposeful creation of an arterio-venous fistula.
In accordance with the invention, there is provided a method for causing arterial blood to flow through a vein of a mammalian patient, in a direction opposite normal venous blood flow, said method comprising the steps of (a) purposefully or inadvertently connecting an arterial blood containing conduit (e.g., an artery, a tubular graft into which arterial blood will flow, a transmyocaridal or interstitial channel that is in fluid communication with a chamber of the left heart or other arterial blood source, etc.) to the vein such that arterial blood will flow from the arterial blood containing conduit into the vein, (b) transluminally inserting a lumen occluding device into the vein, and (c) using the transluminally inserted lumen occluding device to block the lumen of the vein at a location proximal to the location at which the arterial blood containing conduit is connected to the vein (i.e., in a coronary application, between the location at which the arterial blood containing conduit is attached to a coronary vein and the coronary venous sinus into which venous blood drains from the coronary vein). The lumen occluding apparatus used in steps b and c may be any suitable type of transluminally insertable apparatus that will cause a desired degree of blockage or closure of the vein lumen. One type of lumen occluding device that may be used in this method comprises a delivery catheter that deploys a radially expandable blocker device into the lumen of the vein, examples of which are specifically described in this patent application. Examples of other types of transluminally insertable lumen occluding apparatus useable in this method include, but are not limited to those described in U.S. Pat. No. 6,071,292 Makower et al.) entitled Transluminal Methods and Devices for Closing, Forming Attachments to, and/or Forming Anastomotic Junctions in Luminal Anatomical Structures and PCT International Publication Nos. WO97/27893 (Evard, et al.) entitled Methods and Apparatus for Blocking Flow Through Blood Vessels and WO99/49793 (Flaherty et al.) entitled Catheters, Systems and Methods for Percutaneous In Situ Arterio-Venous Bypass, the entire disclosures of which are expressly incorporated herein by reference.
Further in accordance with this invention, there are provided catheter-based devices and systems for implanting radially expandable lumen blocking devices into veins in accordance with the above-summarized method of the present invention. These systems generally comprise (a) a blocker delivery catheter that is transluminally advanced into the vein proximal to the location at which the arterial blood containing conduit is connected to the vein and (b) a radially expandable blocker that is deployable from the catheter such that the blocker radially expands and becomes implanted within the vein at a location proximal to the location at which the arterial blood containing conduit is connected to the vein (i.e., between the location at which the arterial blood containing conduit is attached to the vein and the coronary venous sinus into which venous blood drains from the coronary veins). The blocker delivery catheter may be a relatively long catheter (e.g., 40-125 cm in length) that is inserted into the venous vasculature through a percutaneous puncture site and subsequently advanced transluminally through the venous vasculature to the desired location within the vein. Alternatively, the blocker delivery catheter may be a relatively short catheter (e.g., 5-20 cm in length) that is inserted will into the vein through a small incision or opening created in the vein during a surgical procedure. The same small incision or opening may subsequently be used for attachment all of the arterial blood containing conduit to the vein in accordance with Step (a) of the above-summarized method. The radially expandable lumen blocking device may comprise a generally cylindrical frame that is compressible to a radially compact configuration of a first diameter and is subsequently transitionable to a radially expanded configuration of a second diameter. A flexible or pliable cover (e.g., an obturator) is formed on at least one end of the generally cylindrical frame to block blood flow through the vein when the generally cylindrical frame is radially expanded and implanted within the vein. An opening (e.g., a small hole or slit) may be formed in the cover to permit a guidewire to pass therethrough. In this manner, the blocking device may be initially placed in its radially compact configuration and positioned within the lumen of the delivery catheter. The delivery catheter having the blocker positioned therewithin may be positioned on or advanced over a guidewire such that the guidewire passes through the opening formed in the cover of the blocker. An elongate pusher or other device is then used to expel the blocker from the distal end of the catheter. Thereafter, because the blocker is no longer constrained by the catheter, the cylindrical frame of the blocker self-expands to its radially expanded configuration and the periphery of the blocker becomes firmly coapted with the wall of the vein, thereby holding the blocker in a substantially fixed position within the vein. The guidewire may then be removed, leaving the blocker in place within the vein. Preferably the cover of the blocker is formed of a material that may be punctured or penetrated by a catheter in the event that it is subsequently desired to re-traverse the blocker for the purpose of performing an angioplasty, atherectomy or other catheter-based interventional procedure within the vein, distal to the blocker. If the blocker is re-traversed in this manner, a second blocker may subsequently be placed in the vein proximal to the first blocker, thereby serving to re-occlude the vein after the first blocker has been traversed and rendered ineffective.